1. Field of the Invention
The present invention relates to an image forming apparatus, and particularly to an image forming apparatus that is provided with a print head ejecting liquid droplets.
2. Description of the Related Art
As image forming apparatuses such as printers, facsimile apparatuses, copying apparatuses, plotters, and MFPs combining these functions, there are known, for example, liquid ejection recording type image forming apparatuses, such as inkjet recording apparatuses, which use, as a print head, a liquid ejection head that ejects liquid droplets.
As a method of driving the liquid ejection head in such an image forming apparatus, there is known a method in which, to a pressure generating unit in a head for a nozzle from which no liquid droplet has been ejected (hereinafter referred to as a non-ejection nozzle), a so-called minute-drive waveform is applied, which causes meniscus of the nozzle to vibrate with causing no liquid droplet to be ejected, to maintain the nozzle.
If the minute-drive waveform is applied to all of the nozzles from which no droplet has ejected, large electric power consumption occurs. Therefore, there is known a method to reduce the power consumption by applying the minute-drive waveform only to the non-ejection nozzles that have continued to be in the non-ejection state for a predetermined period of time or by predetermined times.
There is also known an apparatus in which, in order to reduce the power consumption, crosstalk occurring between adjacent liquid chambers is used and the adjacent nozzles are sequentially driven at a slight time difference therebetween so as to obtain a large effect of the minute-drive with a small number of times of the drive (Japanese Patent Application Laid-open No. 2008-229890).
However, there is a problem that increasing the interval of the sequential minute-drive reduces the effect of the minute-drive, and thus makes it impossible to maintain stable droplet ejection characteristics.
In the apparatus that uses the crosstalk, it is necessary to apply a large number of pulses in a short period of time and select pulse for each head. Therefore, there is also a problem that a minute-drive waveform must be generated and switched at a high speed in a very short period of time. There is also a problem that this method cannot be applied to heads that have small crosstalk and thus can perform stable droplet ejection, and therefore can be applied only to heads that have large crosstalk and thus inherently cannot perform stable droplet ejection.
In view of the above-described problems, there is a need to reduce electric power consumption with a simple configuration.